Electric power conversion systems – Current conversion – Including automatic or integral protection means
Patent
1996-02-27
1997-10-07
Wong, Peter S.
Electric power conversion systems
Current conversion
Including automatic or integral protection means
363136, 361 84, H02H 7122, H02H 326, H02M 7521
Patent
active
056754825
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to an accident detection circuit which rapidly detects accidents of a converter due to the arm short-circuit and the like, in a voltage-type self-excited power converter used in a flicker-suppressing device which suppresses flickers of the alternating current-receiving voltage, a reactive power compensating network which compensates the reactive power, and an active filter which suppresses the harmonic of the alternating current-receiving current.
2. Background Art
One example of conventional three-phase voltage-type self-excited power converter comprises 6 arm circuits, and each arm circuit is composed of a power semiconductor element of a self turn off type, a diode connected in anti-parallel to this semiconductor element, and an anode reactor connected in series to the anode of the semiconductor element and for suppressing the current rising rate.
Now, in the voltage-type self-excited power converter having such a structure, when the semiconductor element of the arm circuit on the low voltage side is continued, if the semiconductor element of the arm circuit on the high voltage side is broken or continued due to some misconduct, direct-current short-circuit accident current will flow from the direct-current circuit. Similarly, when both ends of the arm circuit on the high voltage side are short-circuited due to some accident such as flashover, or when short-circuit accidents are caused between lines on the alternating-current side of the converter, similarly the direct-current short-circuit current will flow to the semiconductor element.
Conventionally, in order to detect such accidents and protect the semiconductor element, there have been provided a current detector and an overcurrent relay for every arm circuit. These are to detect the current flowing to the arm circuit by the current detector, to detect when this detected current becomes the overcurrent exceeding a certain value with the overcurrent relay, and to interrupt the short-circuit accident current by giving an off-gate signal simultaneously to all semiconductor elements which constitute the power converter, to protect the power converter.
In said protecting method, there are disadvantages described below. That is, if it is tried to interrupt the current higher than the interruptible current value where there is a current value which can be interrupted as a rating of the semiconductor element by giving the off-gate signal, the semiconductor element will be broken.
Furthermore, in order to output the off signal for interrupting the accident current to the semiconductor element, some periods of time is required, since there is a delay time in the circuit which outputs the off-gate signal.
Therefore, in such accidents, it is required to output the off-gate signal before the accident current reaches the interruptible current value of the semiconductor element after the detection of the accident. Therefore, conventionally, considering the time delay for outputting the off-gate signal after detecting the overcurrent, the anode reactor has been made large to make the rising of the accident current slow. As a result, it leads to the increase of the circuit loss for dealing with the energy of the anode reactor at the time of normal commutation, thereby the efficiency of the power converter decreases.
Or, there is a defect that, in order to interrupt the accident current, semiconductor elements having an interrupting current rating of larger capacity than the interrupting current rating required for interrupting the current flowing at the normal operation must be used.
The object of the present invention is for removing the afore-mentioned defects, and to provide an accident detection circuit of a voltage-type self-excited power converter which can rapidly detect the accident in the self-excited power converter before the short-circuit accident current reaches the overcurrent, and detect the accident in the power converter without making the anode reactor or the power semiconductor element
REFERENCES:
patent: 4546422 (1985-10-01), Okado
patent: 4651270 (1987-03-01), Edwards
patent: 5177428 (1993-01-01), Hirose et al.
patent: 5204563 (1993-04-01), Jason
patent: 5436819 (1995-07-01), Mikami et al.
Inokuchi Haruhisa
Kawakami Noriko
Suzuki Ken'ichi
Kabushiki Kaisha Toshiba
The Tokyo Electric Power Company Incorporated
Vu Bao Q.
Wong Peter S.
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